Electrostatic discharge apparatus for network devices

ABSTRACT

The present invention provides an ESD apparatus that includes an electrical overstress suppression device in series with a capacitor. The ESD apparatus is ideally suited for use with network communication devices, but any electronic device requiring overvoltage protection and isolation may employ the ESD apparatus of the present invention. In one embodiment, the ESD apparatus includes a capacitor and an electrical overstress protection device that electrically communicates in series with the capacitor. In another embodiment, the ESD apparatus includes an electrical overstress protection device having a voltage variable material and a capacitor that electrically communicates in series with the overstress protection device. The capacitor is sized so that the overstress device can withstand an application of a predetermined steady state voltage.

PRIORITY CLAIM

[0001] This application is a non-provisional application claiming thebenefit of U.S. Provisional Patent Application No. 60/304,374, filedJul. 10, 2001, bearing the same title as above and having attorneydocket No. 112690-073.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to overvoltage protection ofelectrically isolated systems. More particularly, the present inventionrelates to an improved electrostatic discharge (“ESD”) apparatus thatmay be employed in Ethernet systems.

[0003] Electrical overstress transients (“EOS transients”) produce highelectric fields and high peak powers that can render circuits, or thehighly sensitive electrical components in the circuits, temporarily orpermanently non-functional. EOS transients can include transientvoltages or current conditions capable of interrupting circuit operationor destroying the circuit outright. EOS transients may arise, forexample, from an electromagnetic pulse, an electrostatic discharge,e.g., from a device or a human body, lightning, a build up of staticelectricity or be induced by the operation of other electronic orelectrical components. An EOS transient can rise to its maximumamplitude in subnanosecond to microsecond times and have repeatingamplitude peaks.

[0004] The peak amplitude of the electrostatic discharge (ESD) transientwave may exceed 25,000 volts with currents of more than 100 amperes.There exist several standards which define the waveform of the EOStransient. These include IEC 61000-4-2, ANSI guidelines on ESD (ANSIC63.16), DO-160, and FAA-20-136. There also exist military standards,such as MIL STD 883 part 3015.7.

[0005] Materials exist for the protection against EOS transients (“EOSmaterials”), which are designed to rapidly respond (i.e., ideally beforethe transient wave reaches its peak) to reduce the transmitted voltageto a much lower value and clamp the voltage at the lower value for theduration of the EOS transient. EOS materials are characterized by havinghigh electrical impedance values at low or normal operating voltages andcurrents. In response to an EOS transient, the materials switchessentially instantaneously to a low electrical impedance state. Whenthe EOS threat has been mitigated these materials return to their highimpedance state. These materials are capable of repeated switchingbetween the high and low impedance states, allowing circuit protectionagainst multiple EOS events.

[0006] EOS materials also recover essentially instantaneously to theiroriginal high impedance value upon termination of the EOS transient. EOSmaterials can switch to the low impedance state thousands of times,withstanding thousands of ESD events, and recover to the high impedancestate after providing protection from each of the individual ESD events.

[0007] Circuit components utilizing EOS materials can shunt a portion ofthe excessive voltage or current due to the EOS transient to ground,protecting the electrical circuit and its components. The major portionof a fast rise time transient, however, is reflected back towards thesource of the threat. The reflected wave is either attenuated by thesource, radiated away, or re-directed back to the surge protectiondevice which responds to each return pulse until the threat energy isreduced to safe levels.

[0008] One electrical device for providing protection against EOStransients is disclosed in U.S. Pat. No. 6,211,554 B1, assigned to theassignee of this invention, and incorporated herein by reference. Onevoltage variable material (“VVM”) or composition for providingprotection against electrical overstress is disclosed in U.S. patentapplication Ser. No. 09/136,507, assigned to the assignee of thisinvention, and is also incorporated herein by reference.

[0009] Typical local area network (“LAN”) design uses an Ethernetprotocol, which usually requires a base band or a broad bandtransmission. Because LAN's typically encompass large distances betweennetwork devices (servers, work stations, printers, etc.), the groundpotential may vary significantly from location to location. This mightresult in data transmission errors and even equipment damage if the datacommunication lines are referenced to earth ground. For this reason,transceivers for LAN and telecom applications are typically differentialmode devices, usually isolated from the network wiring by transformers.These transformers efficiently couple the differential mode data signalsfrom the twisted pair network wiring to the transceiver devices, whileattenuating common mode signals such as those resulting form groundpotential differences.

[0010] Another source of common mode signals are radiated transientsfrom building power lines caused by load switching in equipment such asair conditioners, heaters, elevators, copiers and laser printers. It isalso possible to couple common mode ESD signals to the network wiring bydirect discharge to the cable or a cable connector, or by electric ormagnetic field coupling to the cable.

[0011] Although an ideal transformer would couple a zero common modesignal from the primary (network wiring side) to the secondary (networkdevice transceiver side), real transformers have some capacitancelinking the primary and secondary windings, which allows some commonmode current to flow across the transformer. Common mode chokes anddifferential mode transceivers further attenuate or reject the commonmode signal, but high amplitude, fast rise signals such as thoseresulting from ESD may still cause system malfunction or damage.

[0012] Connection ports on network communication devices must beelectrically isolated according to established standards. For example,Ethernet 10BaseT network communication devices must comply withInternational Standard ISO/IEC8802-3 (ANSI/IEEE Standard 802.3), and100BaseT network communication devices must comply with the standardsset forth in ANSI X3.263-1995, Section 8.4.1 1. For the 10BaseT devices,Standard 802.3 requires that for each PMA/MDI interface, such as thatfound in an RJ-45 connector, the connections to the network wiring mustbe isolated from ground for DC voltage levels as high as 2500 volts.

[0013] Known VVM type ESD apparatuses cannot withstand the presence of ahigh voltage, steady state signal. Other types of ESD protection, suchas spark gaps, are less reliable. Spark gaps are subject toenvironmental conditions, such as heat and humidity. Moreover, sparkgaps can degrade after repeated ESD events. This presents a problem fornetworked communication systems that require ESD protection and highvoltage, direct current isolation. Accordingly, a need exists for areliable VVM type ESD apparatus that can withstand the presence of ahigh voltage (e.g., 2500 VDC), steady state signal.

SUMMARY OF THE INVENTION

[0014] The present invention provides an improved electrostaticdischarge (“ESD”) apparatus. More specifically, the present inventionprovides an ESD apparatus that includes an electrical overstresssuppression device in series with a capacitor. The ESD apparatus isideally suited for use with network communication devices, but anyelectronic device requiring ESD protection and isolation may employ theESD apparatus of the present invention.

[0015] To this end, in one embodiment of the present invention, an ESDapparatus is provided. The ESD apparatus includes a capacitor and anelectrical overstress protection device having a polymeric, non-ohmicvoltage variable material that electrically communicates in series withthe capacitor.

[0016] In an embodiment, the apparatus includes a signal line thatelectrically communicates with the overstress protection device.

[0017] In an embodiment, the signal line Is a data line selected from agroup consisting of 10BaseT, 100BaseT and 1000BaseT data lines.

[0018] In an embodiment, the ESD apparatus includes an Ethernet networkdevice that electrically communicates with the signal line.

[0019] In an embodiment, the ESD apparatus includes a transceiver thatelectrically communicates with the signal line.

[0020] In an embodiment, the ESD apparatus includes an earth ground thatelectrically communicates with the overstress protection device.

[0021] In an embodiment, the capacitor is sized so that the ESD devicecan withstand an application of a predetermined steady state or directcurrent voltage.

[0022] In an embodiment, the capacitor blocks DC current that travelsfrom a signal line to ground.

[0023] In an embodiment, the capacitor couples to an unused data line ofa data transmission connector.

[0024] In an embodiment, the ESD protection device and the capacitor areaffixed to a printed circuit board (“PCB”).

[0025] In an embodiment, the device and the capacitor electricallycommunicate with at least one PCB trace that electrically communicateswith a data transmission connector.

[0026] In an embodiment, the ESD protection device and the capacitor areaffixed to a flexible circuit.

[0027] In an embodiment, the ESD device and the capacitor electricallycommunicate with a spring contact affixed to the flexible circuit.

[0028] In an embodiment, a plurality of EOS devices and capacitorselectrically communicate with a plurality of contacts affixed to theflexible circuit.

[0029] In an embodiment, the EOS device and the capacitor electricallycommunicate with a connector pin of an electrical device.

[0030] In another embodiment of the present invention, an electrostaticdischarge (“ESD”) apparatus is provided. The ESD apparatus includes anon-ohmic voltage variable material (“VVM”) and a capacitor or acapacitor material that electrically communicates in series with theVVM. The capacitor is sized so that the VVM can withstand an applicationof a predetermined steady state voltage.

[0031] In an embodiment, the voltage variable material includes a matrixof conductive and semiconductive particles having an average particlesize of less than 10 microns.

[0032] In an embodiment, the matrix further includes insulativeparticles having an average particle size larger than 300 angstroms.

[0033] In an embodiment, the voltage variable material includesirregularly shaped conductor particles having insulative oxide surfacecoatings that are bound in a matrix.

[0034] In an embodiment, the voltage variable material includes amixture of conductive and semiconductive particles having surfacescoated with an insulative oxide film, the conductive and semiconductiveparticles being bound together in an insulative binder.

[0035] In an embodiment, the voltage variable material includesconductive and semiconductive particles that are coated with aninsulative oxide film and that are bound together in point contact withone another.

[0036] In an embodiment, the voltage variable material includesconductive and semiconductive particles sized to be 10 to 20 microns.

[0037] In an embodiment, the voltage variable material includesparticles sized to be 10 to 20 microns and spaced apart at least 1000angstroms.

[0038] In an embodiment, the VVM and a capacitor or a capacitor materialare placed inside a common housing.

[0039] In an embodiment, the VVM is self-adhering and is self-adhered toa PCB, polymide, flex circuit or inside a housing with a capacitor or acapacitor material.

[0040] In a further embodiment of the present invention, an electricalcircuit for electrostatic discharge suppression is provided. The circuitincludes a signal line and a capacitor that electrically communicateswith the signal line. The circuit includes an electrical overstressprotection device having a polymeric, non-ohmic voltage variablematerial that electrically communicates in series with the capacitor.The circuit also includes an earth ground that electrically communicateswith the overstress protection device.

[0041] In an embodiment, the circuit includes an Ethernet network devicethat electrically communicates with the signal line.

[0042] It is therefore an advantage of the present invention to providean ESD apparatus for use in Ethernet LAN networks.

[0043] Another advantage of the present invention is to provide an ESDapparatus having a steady state blocking function.

[0044] A further advantage of the present invention is to provide an ESDapparatus that can withstand IEEE 802.3 testing and maintain propersuppression of EOS transients.

[0045] Yet another advantage of the present invention is to provide anESD apparatus in which high speed data travels across an aggregatecapacitance that is less than the capacitance of an electricaloverstress protection device that forms part of the ESD apparatus, andwherein the apparatus does not compromise the integrity of the highspeed data.

[0046] Additional features and advantages of the present invention willbe described in, and apparent from, the following Detailed Descriptionof the Preferred Embodiments and the Drawings.

BRIEF DESCRIPTION OF THE FIGURES

[0047]FIG. 1 is a schematic electrical diagram of one embodiment of theimproved ESD apparatus of the present invention.

[0048]FIG. 2 is a fragmentary plan view of a section of a printedcircuit board showing one possible installation for the improved ESDapparatus of the present invention.

[0049]FIG. 3A illustrates a schematic electrical diagram for a knowndata transmission connector.

[0050]FIG. 3B is a schematic electrical diagram illustrating the ESDapparatus of the present invention in combination with data transmissionconnector of FIG. 3A.

[0051]FIG. 4 is a perspective view illustrating the improved ESDapparatus of the present invention employed on a flexible circuit.

DETAILED DESCRIPTION OF THE INVENTION

[0052] Referring now to the drawings and in particular to FIG. 1, aschematic electrical diagram illustrates one embodiment of the improvedESD apparatus of the present invention. It should be appreciated that inone preferred embodiment, the improved ESD apparatus is adapted for usewith a network communication device. Those skilled in the art willrecognize that the apparatus may be used in any electronic systemrequiring ESD transient protection.

[0053] In FIG. 1, an EOS transient voltage 12 enters the circuit 10 onsignal line 14. In normal operation, an overstress protection device 16has a high impedance so that current normally flows to a transceiver 18and not to the protection device 16. Upon the appearance of an EOStransient voltage 12, the protection device 16 switches from the highimpedance state to a low impedance state. A portion of the transientvoltage 12 from the signal line 14 dissipates to the earth ground 20.The protection device 16 reflects most of the transient voltage 12 backtowards the source of the threat.

[0054] In one embodiment, the signal line 14 is a high speed data line,which requires a large frequency band width or operating frequency rangeto allow many carrier frequencies to exist on a single cable. The IEEE802.3 Ethernet specification requires that the ESD apparatus orapparatus 22 be able to withstand 2,250 VDC. The protection device 16 ofthe apparatus 22 cannot withstand this high voltage steady state signal.The apparatus 22 therefore includes a capacitor 24, which is connectedin series with the protection device 16 between the signal line 14 andearth ground 20. In this embodiment the capacitor 24 is placed betweenthe signal line 14 and the protection device 16.

[0055] As is well known in the art, a coupling type capacitor, such ascapacitor 24, allows alternating current to pass through the capacitorbut does not allow DC current to pass through the capacitor, except foran initial surge of current. The protection device 16 can withstand thisinitial burst of current. The capacitor 24 of the apparatus 22, if sizedcorrectly, does not allow the protection device 16 to see the 2,250 VDCsteady state voltage, other than the initial burst of current, becausethe capacitor 24 does not permit DC current to travel to earth ground20.

[0056] The capacitance of capacitor 24 must be properly selected. If thecapacitance is too small, overshoot and undershoot may occur. If thecapacitance is too large, the capacitor 24 absorbs an excessive amountof power. Power dissipation in the capacitor 24 is a function of thefrequency, duty cycle, and bit pattern of the telecommunications data.These factors affect the charging and discharging of capacitor 24 andtherefore the power dissipation capability of the apparatus 22.

[0057] If the capacitor valve is properly selected, however, thecoupling capacitor 24 of the apparatus 22 blocks DC current and therebyprotects the protection device 16 and saves considerable power. Further,an appropriate choice of the capacitor value results in the waveform atthe load end of signal line 14 that is nearly identical to the inputwaveform. That is, the apparatus 22 does not materially alter the shapeor magnitude of the input waveform.

[0058] The apparatus 22 combats both common mode and differential modetransients. In one embodiment, each Ethernet signal line 14 isindividually isolated so that each transceiver 18 is isolated fromdifferential currents flowing between different signal lines 14 and fromcommon mode currents flowing from interconnected leads to ground. Also,because the protection device 16 only shunts a portion of an EOStransient to ground, most of the transient voltage spike 12 is sent backto its source, reducing the occurrence of common mode currents.

[0059] It is well known that capacitors in series add in reciprocal,e.g., 1/Ctotal=1/Ccapacitor+1/Cprotection device. This results in atotal series capacitance that is always less than the smallestcapacitance in the series. The capacitance of the protection device 16is typically significantly smaller than that of the capacitor 24, sothat the total capacitance for the apparatus 22 is roughly the same orslightly less than that of the capacitance of the protection device 16.

[0060] The high speed data that appears on the line 14, to which theapparatus 22 is attached, sees the aggregate capacitance of the twodevices, which is approximately the same or less than that of theprotection device 16 alone. Relative to other circuit protectionmethods, the apparatus 22 should therefore work better as data linesincrease in speed.

[0061] Referring now to FIG. 2, in another embodiment, a plurality ofapparatuses 22 are surface mounted to one side of a PCB substrate 30. Aground bus 20 is soldered to one end of a plurality of capacitors 24, asindicated by the solder joints 34. The capacitors 24 are each soldereddirectly to leads (not illustrated) provided by the overstressprotection devices 16. The overstress protection devices are in turnsoldered to the terminals 32 of a transceiver (not illustrated, can belocated on other side of PCB 30). In one embodiment, the terminals 32electrically connect to a data transmission connector, Such as an RJ-45connector. Methods for surface mounting of the overstress protectiondevice 16 and the capacitor 24 of the apparatus 22 of the presentinvention such as reflow soldering are well known.

[0062] The apparatus 22 illustrated in FIG. 2 has been successfullytested. In testing performed on the apparatus 22, using a PulseGuard®Model PGB002ST23 ESD protection device 16, the protection device 16withstood the required 2,250 VDC steady state voltage for sixty (60)seconds. Moreover, the testing showed that a transceiver chip withstoodrepeated 15 kV air discharge zaps to the data line, e.g., a terminal ofan RJ-45 connector. When an EOS transient voltage 12 occurs, thecapacitor 24 of the apparatus 22 appears as a short with respect to thetransient spike 12, so that the protection device 16 operates asdesigned to protect the transceiver 18. In an embodiment, the capacitor24 is a 1,000 pF capacitor rated for the voltage specified byregulation.

[0063] It should be appreciated that in this embodiment, as opposed tothe embodiment of FIG. 1, the capacitor 24 is positioned between theprotection device 16 and the ground bus 20. The DC coupling capacitor 24disallows DC current to flow from the transceiver terminals 32 to theground bus 20, and thereby protects the protection device 16 from hillDC voltages. Both configurations of the protection device 16 and thecapacitor 24 between signal line and ground serve to protect theprotection device 16 and both configurations are included in the presentinvention.

[0064]FIGS. 3A and 3B illustrate one possible electrical configurationfor the apparatus 22 in the present invention in combination with a datatransmission or RJ-45 connector. FIG. 3A shows a typical configurationfor an RJ-45 connector 40. RJ-45 connector 40 has eight contacts 42 a to42 h. Typically, two contacts, e.g., contacts 42 a and 42 b, connect tosignal transmission lines, while two contacts, e.g., contacts 42 c and42 d connect to signal receiving lines. Four data lines, namely lines 42e through 42 h are typically provided but are unused. Since these linesare unused, they are said to be floating, i.e., they are not fixed viaan input voltage to either a high or low state. Because the data lines42 e through 42 h float, they are each typically electrically coupled toground by a coupling capacitor 24 on a PCB (not illustrated). Thecoupling capacitor 24, as described above, blocks DC current that maydissipate through unused lines 42 e through 42 h and thereby reduces thepower consumption of the system. The capacitor 24 is typically chosen towithstand the DC voltages called out in the IEEE 802.3 Ethernetspecification.

[0065] Many PCB's that contain an RJ-45 connector 40 already include orare specified to include the capacitor 24. FIG. 3B illustrates that theapparatus 22 of the present invention may be readily formed by adding aprotection device 16 in series with the existing capacitor 24. FIG. 3Billustrates that the Rx-data line 42 d electrically connects toprotection device 16, which in turn electrically connects to capacitor24, which in turn electrically connects to earth ground 20. Of course,protection device 16 may alternatively be placed between the capacitor24 and ground 20, as long as the trace or lead 44 is connectedelectrically to the data line 42 d.

[0066]FIG. 3B illustrates that the apparatus 22 protects the singleRx-data line 42 d. It should be appreciated that by extending the traceor lead 44 to any combination or all of the active data lines 42 athrough 42 d, the apparatus 22 of the present invention may protect anynumber of or all of the data lines. FIGS. 3A and 3B are not intended tolimit the application of the present invention to four active datalines; rather, they show one application that makes use of an existingcapacitor 24. If all eight data lines 42 a through 42 h are active, theapparatus 22 may protect any one, a combination of or all eight datalines. Moreover, if desired, the apparatus 22 may be adapted to protectthe inactive data lines 42 e through 42 h illustrated in FIGS. 3A and3B. Moreover, the present invention is not limited to RJ-45 connectorsand is operable with other types of connectors, such as RJ-11, USB andfirewire connectors.

[0067] In another alternative embodiment (not illustrated), a pluralityof apparatuses 22 are employed to protect a combination data lines. Inthis embodiment, each apparatus 22 may protect one or a plurality ofdata lines. For example, one apparatus 22 protects data lines 42 a and42 b, while another apparatus 22 protects data lines 42 c and 42 d. Thisexample may be implemented in a number of ways. In one implementation,the two apparatuses 22 share the same capacitor 24 and the same groundconnection. In another implementation, the two apparatuses each employunique capacitors 24 but use the same ground connection. In a furtherimplementation, the two apparatuses each employ unique capacitors 24 andground connections.

[0068] Referring now to FIG. 4, another application for the apparatus 22includes the installation of the apparatus 22 onto a flexible circuit50. Flexible circuits or “flex circuits” are well known and employ athin, flexible substrate 52 such as Kapton® film. Flex circuits providea convenient means for electrically connecting components located onseparate fixed structures, e.g., PCB's, within a given system. Flexcircuit 50 includes a plurality of spring contacts 54 and at least oneground bus 20. Flex circuit 50 includes a pair of rows of contacts 54and ground buses 20. The present invention is also operable with flexcircuits having other electrical configurations.

[0069] Many types of devices may be coupled to flex circuit 50, wherein,e.g., a flex circuit for connecting to an RJ-45 connector would have atleast eight spring contacts 54, etc. in another configuration, flexcircuit 50 contains the leads or traces 42 a through 42 h (FIGS. 3A and3B) that run to an RJ-45 connector mounted elsewhere on a PCB. Theapparatus 22 can connect to either the illustrated spring contact 54 orto a data line on the flex circuit, similar to the disclosure inconnection with FIGS. 3A and 3B.

[0070] As illustrated, spring contact 54 is in one implementation athrough-hole type of connection, wherein the spring contact 54 receivesa pin 56 of a though-hole type connector or device that is to be mountedto the circuit 50. In another implementation, spring contact 54 isinstead a surface-mount pad, wherein a surface-mount connector reflowsolders to the pad. In either case the spring contact 54 or pad couples,e.g., via solder a joint 34 to the protection device 16 of apparatus 22,which in turn couples, e.g., via a solder joint 34 to the capacitor 24of the apparatus 22, which in turn couples to the ground bus 20. Ofcourse, the order of the protection device 16 and capacitor 24, withrespect to the spring contact 54 (or pad) and the ground bus 20, may bereversed. In either case, capacitor 24 of the apparatus 22 blocks DCcurrent from travelling between the spring contact 54 (or pad) and theground bus 20. The protection device 16 shunts an ESD event to theground bus 20 and/or reflects the signal back towards the source andthereby protects signal lines of the device connected to spring contact54 via one of the pins 56.

[0071] Each of the combinations of apparatuses 22 and data linesdiscussed above in connection with FIGS. 3A and 3B may be employed on aflex circuit. Further, a plurality of apparatuses 22 may exist on thesubstrate 52 to protect a plurality of devices. Further still, one ormore capacitors 24 can operate with a multiple number of devices 16, andthe multiple signal lines of the device may be protected by a singleprotection device 16.

[0072] The protection device 16 contains a voltage variable material(“VVM”). In one embodiment, the VVM includes a composition disclosed inU.S. Pat. No. 6,251,513, entitled “Polymer Composites for OvervoltageProtection”, which includes a matrix of conductive and semiconductiveparticles having an average particle size of less than 10 microns. Thematrix further includes insulative particles having an average particlesize larger than 300 angstroms. VVM's utilizing relatively smallparticle sized conductive and semiconductive fillers exhibit clampingvoltages in a range of about 30 volts to about 2,000 volts or greater.In other embodiments, the protection device 16 can include any knownvoltage variable material. Specifically, the voltage variable materialsmay include any of the following compositions, which are incorporatedherein by reference.

[0073] U.S. Pat. No. 2,273,704, issued to Grisdale, discloses granularcomposites which exhibit non-linear current/voltage relationships. Thesemixtures are comprised of conductive and semiconductive granules thatare coated with a thin insulative layer and are compressed and bondedtogether to provide a coherent body.

[0074] U.S. Pat. No. 2,796,505, issued to Bocciarelli, discloses anon-linear voltage regulating element. The element is comprised ofconductor particles having insulative oxide surface coatings that arebound in a matrix. The particles are irregular in shape and make pointcontact with one another.

[0075] U.S. Pat. No. 4,726,991 issued to Hyatt et al., discloses an EOSprotection material comprised of a mixture of conductive andsemiconductive particles, all of whose surfaces are coated with aninsulative oxide film. These particles are bound together in aninsulative binder. The coated particles are preferably in point contactwith each other and conduct preferentially in a quantum mechanicaltunneling mode.

[0076] U.S. Pat. No. 5,476,714, issued to Hyatt, discloses EOS compositematerials comprised of mixtures of conductive and semiconductiveparticles sized to be in a 10 to 100 micron range. The materials alsoinclude a proportion of 100 angstrom sized insulative particles. All ofthese materials are bonded together in a insulative binder. Thisinvention includes a grading of particle sizes such that the compositioncauses the particles to take a preferential relationship to each other.

[0077] U.S. Pat. No. 5,260,848, issued to Childers, discloses foldbackswitching materials which provide protection from transientovervoltages. These materials are comprised of mixtures of conductiveparticles in the 10 to 200 micron range. Semiconductor and insulativeparticles are also employed in these compositions. The spacing betweenconductive particles is at least 1000 angstroms.

[0078] Additional EOS polymer composite materials are also disclosed inU.S. Pat. Nos. 4,331,948, 4,726, 991, 4,977,357, 4,992,333, 5,142,263,5,189,387, 5,294,374, 5,476,714, 5,669,381 and 5,781,395, the teachingsof which are specifically incorporated herein by reference.

[0079] The above embodiments have been illustrated and described asincluding an apparatus 22 of the present invention, which includes anEOS device 16 and a capacitor 24. This implies that apparatus 22includes at least two separate devices 16 and 24. As illustrated,apparatus 22 can include a separate EOS device 16 and a separatecapacitor 24, which is typically provided in the form of a device. Asillustrated in connection with FIG. 3B, it may be desirable to couple anEOS device 16 to a capacitor 24 that already exists on a PCB.

[0080] In other embodiments, a capacitor or a capacitor material, e.g.,a semi-conductive material, and an EOS material may be packaged in asingle housing, wherein the capacitor or the capacitor material and theEOS material communicate via at least one electrode. In still anotherembodiment, a directly applicable voltage variable material (“VVM”) setforth in Provisional U.S. Patent application No. 60/370,975, entitled“Voltage Variable Material for Direct Application and Devices EmployingSame”, assigned to the assignee of this invention, may be employed. ThisVVM material does not have to be provided in a housing and may thereforebe applied directly to a substrate, cured or not cured and then perhapsencapsulated via an epoxy coating. This VVM intrinsically adheres tosurfaces, such as a conductive, metal surface or a non-conductive,insulative surface or substrate, and cures without additionalprocessing. Applications using this VVM can be cured however to speedthe manufacturing process of same.

[0081] The self-curing and self-adhering insulative binder of the VVMdisclosed in Provisional Patent application No. 60/370,975 includes apolymer or thermoplastic resin, such as polyester, which is dissolved ina solvent. The polyester resin has a glass transition temperature in therange of 6° C. to 80° C. and a molecular weight between 15,000 and23,000 atomic mass units (“AMU's”). One suitable solvent for dissolvingthe polymer is diethylene glycol monoethyl ether acetate, commonlyreferred to as “carbitol acetatate”. In an embodiment, a thickeningagent is added to the insulative binder, which increases the viscosityof the insulative binder. For example, the thickening agent can be afumed silica, such as that found under the tradename Cab-o-Sil TS-720.

[0082] The insulative binder of the present invention has a highdielectric breakdown strength, a high electrical resistivity and hightracking impedance. The insulative binder provides and maintainssufficient interparticle spacing between the other possible componentsof VVM 100, such as conductive particles, insulating particles,semiconductive particles, doped semiconductive particles and variouscombinations of these. The interparticle spacing, the resistivity anddielectric strength of the insulative binder each affect the highimpedance quality of the VVM in its normal state. In an embodiment, theinsulative binder has a volume resistivity of at least 10⁹ ohm-cm. It ispossible to blend different polymers in the binder and to cross-linksame.

[0083] It should be understood that various changes and modifications tothe presently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications may be madewithout departing from the spirit and scope of the present invention andwithout diminishing its attendant advantages.

The invention is claimed as follows:
 1. An electrostatic discharge(“ESD”) apparatus comprising: an electrical overstress (“EOS”)protection device having a non-ohmic voltage variable material; and acapacitor that electrically communicates in series with the protectiondevice.
 2. The ESD apparatus of claim 1, which includes a signal linethat electrically couples to one of the EOS protection device and thecapacitor.
 3. The ESD apparatus of claim 2, wherein the signal line isselected from a group consisting of 10BaseT, 100BaseT and 1000BaseT datalines.
 4. The ESD apparatus of claim 2, which includes an Ethernetnetwork device that electrically communicates with the signal line. 5.The ESD apparatus of claim 2, which includes a transceiver thatelectrically communicates with the signal line.
 6. The ESD apparatus ofclaim 1, which includes a ground that electrically communicates with oneof the EOS protection device and the capacitor.
 7. The ESD apparatus ofclaim 1, wherein the capacitor is sized so that the EOS protectiondevice can withstand an application of a predetermined direct currentvoltage.
 8. The ESD apparatus of claim 1, wherein the capacitor blocksDC current that travels from a signal line to ground.
 9. The ESDapparatus of claim 1, wherein the capacitor couples to an unused dataline of a data transmission connector.
 10. The ESD apparatus of claim 1,wherein the EOS protection device and the capacitor are affixed to aprinted circuit board (“PCB”).
 11. The ESD apparatus of claim 1, whereinthe EOS protection device and the capacitor electrically communicatewith at least one PCB trace, and wherein the trace communicateselectrically with a data transmission connector.
 12. The ESD apparatusof claim 1, wherein the capacitor additionally serves to reduce powerconsumption.
 13. The ESD apparatus of claim 1, wherein the EOSprotection device and the capacitor are affixed to a flexible circuit.14. The ESD apparatus of claim 13, wherein the EOS protection device andthe capacitor electrically communicate with a spring contact affixed tothe flexible circuit.
 15. The ESD apparatus of claim 13, wherein the EOSprotection device and the capacitor electrically communicate with aconnector pin of an electrical device.
 16. The ESD apparatus of claim13, wherein a plurality of EOS devices and capacitors electricallycommunicate with a plurality of contacts affixed to the flexiblecircuit.
 17. An electrostatic discharge (“ESD”) apparatus comprising: apolymeric composite voltage variable material (“VVM”); and a capacitormaterial that electrically communicates in series with the VVM, thecapacitor material sized so that the VVM can withstand an application ofa predetermined direct current voltage.
 18. The ESD apparatus of claim17, wherein the VVM includes a matrix of conductive and semiconductiveparticles.
 19. The ESD apparatus of claim 17, wherein the VVM includesirregularly shaped conductor particles having insulative oxide surfacecoatings that are bound in a matrix.
 20. The ESD apparatus of claim 17,wherein the VVM includes a mixture of conductive and semiconductiveparticles having surfaces coated with an insulative oxide film, theconductive and semiconductive particles being bound together in aninsulative binder.
 21. The ESD apparatus of claim 17, wherein the VVMincludes conductive and semiconductive particles that are coated with aninsulative oxide film and that are bound together in point contact withone another.
 22. The ESD apparatus of claim 17, wherein the VVM includesconductive and semiconductive particles sized to be 10 to 20 microns.23. The ESD apparatus of claim 17, wherein the VVM self-adheres directlyto a substrate.
 24. The ESD apparatus of claim 17, wherein the VVM isdisposed inside a housin with the capacitor material.
 25. The ESDapparatus of claim 17, wherein the VVM is disposed inside a housing witha capacitor that holds the capacitor material.
 26. An electrical circuitfor electrostatic discharge suppression comprising: a signal line; anon-ohmic voltage variable material (“VVM”) that electricallycommunicates with the signal line; a capacitor that electricallycommunicates in series with the VVM; and a ground that electricallycommunicates with the capacitor.
 27. The electrical circuit of claim 26,which includes an Ethernet network device that electrically communicateswith the signal line.
 28. The electrical circuit of claim 26, whereinthe capacitor additionally serves to reduce power consumption.
 29. Theelectrical circuit of claim 26, wherein the VVM is disposed in a mannerselected from the group consisting of: in a device, on a flex circuitand applied directly to a substrate.